1. Field of the Invention
This invention relates to methods of forming beam blanks, and more particularly to a method of forming a beam blank suitable for use in producing by rolling a beam blank used for rolling a shape steel having a web and flanges.
2. Description of the Prior Art
Heretofore, a beam blank used for rolling a shape steel having a web and flanges such as I-steel or H-steel has been obtained from an ingot after carrying out many passes in blooming mill. Namely, the method of rolling such a beam blank as described above has been effected by a high lift-two high reversible blooming mill with the upper and lower horizontal rolls being provided with a plurality of calibers, and the general procedures of rolling have been as shown in FIG. 1. More specifically, firstly, an ingot 10 being of a rectangular parallelepiped as shown in FIG. 1(A) is rolled to be as flat as a material body 16 having a rectangular cross section introducible to beam blank calibers 12-2, 14-2 by means of bullhead calibers 12-1, 14-1 of working rolls 12, 14, as shown in FIG. 1(B), subsequently, as shown in FIG. 1(C), is caliber-rolled by means of the beam blank calibers 12-2, 14-2 to provide a beam blank 18 having a predetermined shape in cross section as shown in FIG. 1(E). Overfills 16a of the material body come out of the side surfaces 12-2a, 14-2a of the beam blank calibers 12-2, 14-2 during passes under said caliber rolling, and hence, edging rolling is carried out to flatten overfills 16a by means of box calibers 12-3, 12-4 at suitable times as shown in FIG. 1(D). Furthermore, during the rolling as described above, flange portions 16b of the material body 16 are elongated simultaneously with a web portion 16c under the influence of elongation of the web portion 16c, and hence, in order to fill the flange portions 12-2, 14-2 of the beam blank calibers with the material body 16 during caliber rolling it is necessary that the height H of the material body 16 in rectangular cross section should be increased with the increase in the width h of the flange of the beam blank. In general, it is necessary that the ratio between the height H of the material body 16 in rectangular cross section and the width h of flange of the beam blank 18 should be more than two.
However, with the conventional method of rolling as described above, there have been disadvantages as shown below.
(1) Increased number of passes is required to obtain the beam blank 18 from the ingot 10. Further, increased number of turning is required for edging rolling by use of the box calibers 12-3, 14-3, thus resulting in lowered rolling efficiency.
(2) A high reduction value for the web portion 18c is required as compared with the reduction value for the flange portions 18b, with the result that the value of elongation of the web 18c becomes larger than that of the flange portions 18b to a considerable extent, whereby a web tongue 18d shown in FIG. 2 becomes large which should be cut away, thus resulting in lowered yield.
(3) A high reduction value for the web portion 18c is required as compared with the reduction value for the flange portions 18b, with the result that the roll-away of the surface defects such as below holes, skin holes and side cracks is not enough at the flange portions 18b, thus requiring working for removing the surface defects on the finished beam blank 18.
On the other hand, in rolling a plate or the like, there has recently been developed such a method that the process of ingot forming.fwdarw.soaking.fwdarw.blooming is omitted and a plate-shaped slab for a plate is produced by continuous casting. Said production of the slab by the continuous casting can offer various advantages including save of thermal energy, improved internal quality of the material and also improved yield, and hence, to obviate the abovedescribed disadvantages, such a method has been practised as to produce by the continuous casting a beam blank having a section approximating to FIG. 1(E). However, said method requires high installation costs to fulfill the requirements of production of various shapes in cross section of the beam blanks, and hence, with shape steels having an identical cross section with one another in a large amount of production, high profits can be expected, however, with beam blanks having various cross sections each in a small amount of production such as H-steels having large cross section, respectively, only decreased profits are expected.
Then, there has been proposed a method wherein a plate-shaped slab easily produced by continuous casting is rolled by means of roughing mill in a shape steel shop to provide a beam blank 18 as shown in FIG. 1(E).
As shown in an example of Japanese Patent Publication No. 567/70, as a method of rolling a plate-shaped slab to provide an H-steel, there has been proposed a method wherein the reduction-rolling in the widthwise direction of the slab (hereinafter referred to as the "edging rolling") is performed on a plate-shaped slab by means of working rolls each having an edging caliber, whereby side spreadings are generated at opposite end portions of the slab in the widthwise direction, to thereby provide a beam blank being of a dog-bone shape in cross section.
On the other hand, in general, in the case the edging rolling is performed on an elongated material, to prevent the material from falling down or being distorted due to the edging rolling, the elongated material is often rolled by use of box calibers each having a width of the bottom of caliber substantially equal to the width of the material body and a large depth. However, if the width of the caliber is decreased, then the side spreadings of the material body is regulated, and consequently, a necessary width of flange cannot be obtained. According to the aforesaid Japanese Patent Publication No. 567/70, to obtain a necessary width of flange, the edging rolling is performed by use of only the working rolls each having a pair of shallow edging caliber. In this case, however, not only the material being rolled is unstabilized in its posture, but also the material body side-spreaded is forced out of the caliber, thus causing overlaps.